Packet transmission system and method utilizing both a data bus and dedicated control lines

ABSTRACT

A common communication controller is linked to a plurality of peripheral devices by a network interface bus. Packets containing information is communicated between the controller and the peripherals over the bus which consists of a parallel packet bus and a plurality of control lines utilized to implement a communication protocol which increases the efficiencies of packet communications by the utilization of additional direct command lines between the communications controller and peripherals.

FIELD OF THE INVENTION

This application is a Continuation-In-Part of application Ser. No.07/414,792 filed Sep. 29, 1989 and now abandoned, application Ser. No.07/445,238 filed Dec. 4, 1989 and now abandoned, application Ser. No.07/645,383 filed Jan. 24, 1991 and now abandoned, application Ser. No.07/646,924 filed Jan. 28, 1991 and now abandoned, application Ser. No.07/682,486 filed Apr. 24, 1991 and now abandoned.

This invention pertains to a voice/data packet transmission system andis especially suited for a packet transmission system which mustaccommodate a variety of different peripheral devices.

BACKGROUND OF THE INVENTION

Voice and data switches are known in the prior art. Packet switching isalso known. In the past, however, synchronization for the control of thedevices sending and receiving information packets in a voice/data packetswitch has been a problem. This problem has been related to the problemof dynamically allocating the packet bandwidth between the variousperipheral devices attached to the switch for voice information and datainformation. Another related factor has been the network interfacearchitecture for the switch. The network interface architectures of pastswitches have used the same bus for both data and control. When coupledwith the problem of dynamically allocating bandwidth on the bus, thisnetwork interface architecture has resulted in the switch having a lowswitching capacity and throughput. These performance problems becomeeven more significant in the context of modern fast packet protocols. Itwould be desirable, therefore, to provide a voice/data packet switchwith an improved network interface architecture.

In a synchronous system a clock signal corresponding to intervals ofdata transmission is either made directly available to terminals withinthe network or it is derived from signals sent by the transmittingterminal. In such a system, a master terminal defines the clockinformation which is derived by slave terminals. Mainframe computernetworks which maintain constant communication with slave devices are anexample of such networks.

Asynchronous communications differ in that clock information is notprovided. Another mechanism must be utilized in order to define thebeginning and end of each character or period. In modem networks startand stop bits are utilized by the transmitting modem so that thereceiving modem can identify the beginning and end of a transmittedcharacter.

In a TDMA packet network in which each frame contains a plurality oftime slots allocated for different users or purposes, it is criticalthat the receiving terminal be able to properly correlate the beginningof each frame and of each time slot in order to properly decode thetransmitted information. It is known in packet systems to utilize a timestamp which is transmitted as part of the packet. For example, see U.S.Pat. No. 4,530,091 and U.S. Pat. No. 4,894,823.

In a wireless packet TDMA system, two types of synchronization isrequired. First, the beginning of each frame and each time slot (packet)within each frame must be identified. Such identification can beaccomplished by transmitting a known data pattern for a predeterminednumber of bits. This pattern is recognized by the receiving terminal andthe beginning of the frame or packet is determined. In a TDMA network inwhich a master node defines the frame and packet timing for remoteterminals, each terminal must be aligned in time relative to the startof the node frame in order to properly receive and transmit informationat a predefined time slot within the frame. Problems in acquiring andmaintaining this type of synchronization exist especially in a wirelessTDMA packet network in which different directional antennas are used forcommunications. Thus there exists a need for an improved method formaintaining time synchronization in a wireless TDMA packet network inwhich multiple antennas are utilized.

Packet data networks convey information from an originator to aspecified addressee by incorporating the information into packets. Eachpacket contains a preamble (control data) and information (messagedata). The preamble typically includes packet network control data,synchronization information, and addressee destination information. Theinformation portion contains part of the total originator's message.

The packet originated by the addressor is typically not directlyreceived by the addressee. The packet may be relayed by severalintermediate stations before reaching the final addressee destination.As the transmission speeds of packet networks increase, it becomesincreasingly important for relay stations to be able to efficientlyhandle and process packets.

In a direct method for handling packets, received packets are stored ina memory location. The destination of the packet contained at thepreamble is checked as well as other packet network control information.Correct receipt or validation of the control information and the packetdata information is checked. Assuming no errors are detected, a newpacket corresponding to the received packet is created and stored in adifferent memory location for transmission. At the appropriate time, thereconstituted packet is retransmitted by the relay station towards itsfinal destination.

Packets are handled in a different manner in an Ethernet local areanetwork. A buffer ring structure comprised of a series of contiguousfixed length byte buffers are utilized for storage of received packets.The beginning and end location of the stored packet is identified byaddresses held in a page start and a page stop register. Successivebuffers in the ring are utilized to store the packet. Multiple packetscan be consecutively stored in the ring structure. The packets arenormally removed from the receive buffer ring in FIFO order and arereconstituted for retransmission in memory separate from this ring.

There exists a need for an improved method for organizing and handlingpackets that minimizes intermediate data transfer to additional memorylocations prior to retransmission of the packet

Packet protocols become increasingly inefficient as the amount of datato be transmitted per packet decreases because of the required packetoverhead required for each packet. Although short commands can betransmitted from one point to another using packets, a substantial delayexists before the receiving device can act upon the command due to thetime requirements of packet transmission and packet disassembly beforethe command can be forwarded to the destination device.

In a conventional direct control systems each function to be controlledis assigned a separate wire or communication channel which carries apredetermined command from a controller to the device implementing thefunction. Such systems exist for a variety of applications and areefficient where a limited number of commands are to be transmitted tospecific devices. These systems become increasingly complex as thenumber of commands and devices to be controlled increase. No addressingis required in these systems since each dedicated path has a preassignedsingle function to control.

There exists a need for a system and method which can carry informationutilizing packets while minimizing the inefficiencies related to thetransmission of commands to associated devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a packet/fast packet switch for voiceand data.

FIG. 2 shows the network interface bus for the first embodiment.

FIG. 3 shows a packet.

FIG. 4 is a high-level block diagram for the network interface.

FIG. 5 shows a network interface memory map.

FIG. 6 shows address registers.

FIG. 7 shows processor data memory area for the network interface.

FIG. 8 shows network interface base registers.

FIG. 9 shows a status/control register.

FIG. 10 shows a virtual circuit register.

FIG. 11 is a timing diagram showing the network interface controltransfer timing.

FIG. 12 is a timing diagram showing a data transfer from a device to thenetwork interface with no additional bytes.

FIG. 13 is a timing diagram showing a data transfer from a device to thenetwork interface with additional bytes.

FIG. 14 is a timing diagram showing a data transfer from the networkinterface to a device.

FIG. 15 is a timing diagram showing a data transfer from a device to thenetwork interface with a maximum packet size error or a space availableerror.

FIG. 16 is a timing diagram showing a data transfer from a device to thenetwork interface with a CRC error.

FIG. 17 is a timing diagram showing a data transfer from a device to thenetwork interface with an address error.

FIG. 18 illustrates a format for information in one time slot in apacket environment.

FIG. 19 illustrates the information contained in the packet header asshown in FIG. 18.

FIG. 20 is a diagram representing the packet addressing method andorganization in accordance with the present invention.

FIG. 21 illustrates the contents and format for the virtual circuitregister as shown in FIG. 20.

FIG. 22 shows the content and format of the queue control block as shownin FIG. 20.

FIG. 23 shows the contents and format of a packet descriptor as shown inFIG. 20.

FIG. 24 shows the contents and format of a buffer descriptor as shown inFIG. 20.

FIG. 25 is a diagram illustrating an exemplary wireless TDMA packetnetwork incorporating the present invention.

FIG. 26 is a block diagram illustrating control modules and user modulesutilized in the packet system as shown in FIG. 25.

FIG. 27 is a flow diagram illustrating the generation of framesynchronization packets by the control module.

FIG. 28A illustrates the format of a frame synchronization packetgenerated by the control module.

FIG. 28B illustrates the format of one frame as defined by the controlmodule.

FIG. 28C illustrates the format of a frame as received by a user module.

FIG. 29 is a flow diagram illustrating the generation of a frame startinterrupt by a user module.

FIG. 30 is a flow diagram of the steps used in the user module fordetermining the frame time synchronization relative to the controlmodule frame.

FIG. 31 is a flow diagram of the steps taken by the user module foradjusting a received frame to maintain time synchronization with thecontrol module frame.

FIG. 32 illustrates a wireless packet communication system suited forincorporating the present invention.

FIG. 33 illustrates a packet format utilized in a preferred embodimentof the present invention.

FIG. 34 is a flow diagram illustrating the transmission of data from acommunication controller to a peripheral device.

FIG. 35 is a timing diagram illustrating control signals utilized inaccordance with the flow diagram of FIG. 34.

FIG. 36 is a flow diagram illustrating the transmission of data from aperipheral device to the communication controller.

FIG. 37 is a timing diagram illustrating controls utilized to transmitinformation in accordance with the steps of FIG. 36.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, it is seen that the Network Interface 105 isthe focus of the LAN device (both Node and UM). It connects the variousinterfaces on the LAN (both cable and radio) to one another and to theControl Processor 107, providing time-division and fast-packetswitching. Information is transferred among these interfaces via theNetwork Interface Memory 111 that is accessible both by the controlsections of the Network Interface (both input and output), and by theControl Processor 107. The memory 111 preferably consists of a controlmemory portion and a data memory portion. Information flow on the LANside is via the Network Interface Bus (NI-Bus) 101, which is designed topass data at rates up to, for example, 5 million bytes per second, andto handle the corresponding control information at a similar rate. Themicroprocessor bus 103 couples the network interface 105 to the controlprocessor 107, hereinafter collectively referred to as thecommunications controller.

Referring now to FIG. 2, the interaction between the Network InterfaceMemory 111 and the NI-Bus 101 is shown. The Output Control circuitry 206of the Network Interface chip 109, sequentially steps through theControl memory 211 and presents address and command bytes to the ControlBus 203. This information controls which device is driving the NI-Bus101 and which device is listening. All NI-Bus devices, including theNetwork Interface 105, listen to the Control Bus 203 to determine whatthe activity is on the Data Bus 201. The Output Control circuitry alsosequentially steps through the Data memory. If the Network Interface 105is driving the bus 101, the information in the Data memory 213 will beoutput to the Data Bus 201. If the Network Interface 105 is listening tothe Data Bus 201, the Input Control 205 will accept the data and put itin the proper area of Network Interface Memory 111. The NetworkInterface 105 can both listen and drive the bus 101 at the same time.This allows the Network Interface 105 to be put in a loopback mode.

FIG. 3 shows the configuration of a standard packet 300. When a startpacket signal (described in a later section) is received from a NI-Bus101 peripheral (for instance, the radio link 125, 127, 129), the firstbyte 301 received by the Network Interface is the Virtual Circuit ID.This field 301 is used to make a pointer into an area of NI-Memory 111that holds control information for up to 256 virtual circuits--primarilypacket destination addresses. The Input Control uses this information tostore the packet information field in the appropriate location inNI-Memory.

The Packet Length field 303 is evaluated next, and checked against theMax Packet Size field in the appropriate Virtual Circuit Register,described in a later section. If the Packet Length is greater than theMax Packet Size, the Info field of the packet will not be stored.

The Address Type field 305 is used as an offset into a field of 16device Address Registers, each up to 128 bits long. The appropriateAddress Register, described in a later section, is then compared againstthe Address field 309 in the received packet, up to the number of bytesindicated in the Address Length field 307 of the packet. If the address309 does not match, the Info field 313 is not stored. Note than anaddress of zero length is always seen as a match, and thus represents anall call.

The CRC checker, in the Network Interface, will check the CRC for theentire packet header including the Header FCS 311. The result of thechecker will be zero for a valid header. If the CRC check is invalid,the Network Interface will generate a Packet End signal.

Three conditions must be met in order for the Network Interface 105 tostore the Info field into NI Memory 111:

1. The Packet Length 303 in the packet header 315 must be less than orequal to Max Packet Size stored in the Virtual Circuit Register.

2. The Address 309 in the packet header 315 must be equal to the addresscontained in the Address Register defined by the Address Type 305 forthe number of bytes defined by the Address Length 307. Note: The twoaddresses need not be inherently the same. This allows Group Calls.

3. The CRC check must be valid.

All of these memory areas are defined in a set of NI Base Registers,described in a later section, that are accessible to the ControlProcessor 107.

Thus, the Control Processor 107 completely defines the output areas ofthe frame, and the timing and device selection of input areas. It writesthe necessary data into the Control area 211, and, where appropriate,puts data into the Data area 213--for instance, the appropriate headersto be transmitted.

Then, the Control Processor 107 sets up the appropriate addresses (readinitially from a personality module containing, among other things, theElectronic Serial Number of the particular device), establishesappropriate Virtual Circuit parameters (e.g., a data packet interface tothe Control Processor), and sets the appropriate pointers in the BaseRegisters.

Referring to FIG. 4 there is shown the network interface 105. TheNetwork Interface is made up of six basic blocks: Input 405, Output 407,NI-Bus Decode 409, Memory Access Control 403, Processor Interface 207,and Memory 111. The memory 111 is not currently contained in the NetworkInterface ASIC 109.

The Input block 405 evaluates the header of the incoming packet anddetermines what to do with the packet. When a Packet Start indication417 is received along with the Data Clock 419, the Input section 405loads the header 315 and determines if the packet 300 is for this deviceand determines the routing. Once the routing is determined, theinformation field of the packet is loaded into the proper area in theNetwork Interface memory 111.

The Input block 405 is connected to the outside world via an 8-bit widebi-directional data bus, the Network Interface Data Bus 201. The NI DataBus 201 has a maximum clock rate of 5 MHz. The Data Clock signal 419indicates when the data is stable. The Packet Start signal 417, inconjunction with the Data Clock signal 419, indicates the first byte ofa packet 300. The data bus 201 is the same bus that is connected to theOutput block 407. The Network Interface 105 is only able to input fromor output to a single interface device at any given time. The Packet Endsignal 421 is generated by the Network Interface when it has receivedthe last byte of the packet indicated by the Packet Length 303 containedin the packet header 315. This signal 421 is used by the interfacedevices to determine when additional bytes, such as signal strengthinformation, are to be sent to the Network Interface 105.

Timing for the NI-Bus 101 signals can be found in FIGS. 11-17.

The Input block 405 can address up to 62 interface devices; however, thebus loading limit is 12. The interface devices include radio, LAN, andphone interfaces. Time is allocated during each frame via the NI ControlBus 203 to allow these devices to pass packets between one another.

The Output block 407 performs two major functions. First, it outputspackets from the Network Interface 105 to the interface devices on theNI Data Bus 201 at the proper time during a frame. Secondly, it outputsthe control information on the NI Control Bus 203. The NI Control Bus203 is an 8-bit wide bus at a maximum clock rate of 5 MHz. The ControlClock signal 427 indicates when the control bus 203 is stable, and theData Clock 419 indicates when the data bus 201 is stable. The Outputblock 407 cycles through the Data and Control Buffers at the clock ratedetermined by the Clock Divisor in the NI Base Registers. The positionin the Data Buffer is synchronized to the position in the frame via theSync Offset in the NI Base Registers.

The NI-Bus Decode 409 listens to the addresses and commands on theNI-Bus 101. It decodes all commands that have a broadcast or NetworkInterface address. It provides control to the Input block 405 to tell itwhen to listen to the Data Bus 201 and to the Output block 407 to tellit when to drive the Data Bus 201. It also decodes the Skip N Clockscommand for the Output block 407.

The Processor Interface block 207 provides the interface between theControl Processor 107 and the Network Interface 105. It also containsthe NI Base Registers described in a later section. The ControlProcessor 107 has to read/write from/to the memory and registers in theNetwork Interface 105. The Processor Interface 207 allows the ControlProcessor 107 to access the memory/registers without slowing down theoperation of the Network Interface 105. Zero to two wait states may beinjected, via DTACK, due to the frequency of Control Processor 107memory accesses allowed by the Network Interface 105. DTACK is generatedfor both read and write.

The network interface 105 will occupy a 64K byte space in the ControlProcessor 107's memory map. The NI Base Registers occupy address hexFC00 through hex FC17 in this space. The Processor Interface 207 willsupport both byte and word operations on the NI registers and memory.The NI Memory 111 is organized the same way as the 68000 memory.

The Network Interface 105 can interrupt the Control Processor 107 viathe INT line. The INT line will be cleared when the Control Processorresponds with an interrupt acknowledge, ITACK. The NI 105 has twosources of interrupts. The first is at the start of the frame, and thesecond is the reception of a packet destined for the Control Processor107. These interrupts can be enabled and disabled by software.

The Network Interface 105 can be reset via a Reset Line from theProcessor 107. This must be part of the power-up sequence. The endresult of an NI reset is to guarantee the Control bus 203 will notoutput any commands. The reset is active low and must be low for atleast 1 microsecond.

The definition of the signals contained in the processor interface 207to the NI 105 can be found in FIGS. 11-16.

The Memory Access Control block 403 allocates the appropriate number ofNetwork Interface Memory 111 accesses to the Input 405, Output 407, andProcessor Interface 207 blocks. Each block requires a certain maximumnumber of memory accesses during a byte time (200 nanoseconds). Eachblock has its maximum number of memory accesses allocated to it everybyte time.

The Memory block 111 provides all memory that is required by the NetworkInterface 105. It not only contains memory for the packets, but alsomemory for the registers that are required for routing and addressing inthe Network Interface 105.

Refer to FIG. 5, which shows a memory map 500 of the memory 111. Thememory 111 is divided into five sections: Virtual Circuit Registers 501,Address Registers 503, Processor Data 505, Control Buffer 509, and DataBuffer 507. The header 315 of the incoming packet 300 containsinformation that, when used in conjunction with the Virtual CircuitRegisters and Address Registers, determines the route of the packetthrough the Network Interface 105. The standard packet 300 is shown inFIG. 3.

The Network Interface 105 can interrupt the Control Processor 107 viathe INT line. The INT line will be cleared when the NI receives aninterrupt acknowledge, ITACK. The NI can generate two types ofinterrupts. The first is one at the beginning of every frame. The secondis when a packet is received destined for the Control Processor 107.Either one of these interrupts can be disabled by software via theStatus/Control Register 900.

The Virtual Circuit Registers 501 are used with the Circuit ID field 301of an incoming packet 300 to determine where in memory 111 the packet isto be stored. There are a total of 256 Circuit IDs, of which some arereserved for special packets such as reset, frame sync and control data.The Circuit ID 301 contained in the packet is used in conjunction withthe Virtual Circuit Register Pointer in the NI Base Registers todetermine the address of the Virtual Circuit Register. The contents ofthe Virtual Circuit Register is used to determine the routing andcharacteristics of the packet.

The next section of memory is the Address Registers 503. This sectioncontains 128-bit registers. This allows a device to have multipleaddresses of multiple types. The layout 600 of the Address RegisterMemory 503 is shown in FIG. 6. A device can have sixteen differentaddresses of varying types, and these addresses can change. 128 bits waschosen because of the requirement of a unique electronic serial numberfor each device.

An incoming packet 300 contains an Address Type 305, Address Length 307,and Address 309. The Address Type 305 is used in conjunction with theAddress Register Pointer in the NI Base Registers to determine theaddress of the proper Address Register in memory. The Address Length 307is used to determine how many bytes of the Address Register are readfrom memory. The bytes read from memory are then compared to thecontents of the Address field 309 in the incoming packet. Thisdetermines if the packet is being sent to this device. Note that anaddress of zero length is always seen as a match, and thus represents anall call.

Referring again to FIG. 5, the Processor Data 505 section of memoryprovides storage for all incoming packets that are destined for theControl Processor 107. The management of this section of memory is morecomplex than the other sections. It is necessary to store multiplepackets in this area of memory during a single frame. The types ofpackets stored in this section of memory are frame sync, control, casualdata, and LAN data.

A circular buffer is used for the Processor Data section of memory 505.It is implemented using pointers in the NI Base Registers. A diagram 700of the Processor Data 505 section of memory is shown in FIG. 7.

The organization of the packet storage in the Processor Data buffer isalso shown in FIG. 7. The following is a list of the information storedin the buffer for each packet, and the order in which it is stored:

1. The number of bytes of additional information that are storedfollowing the Info field of the packet. (1 byte)

2. The length of the Info field of the packet. (2 bytes)

3. The Info field of the packet. (0-2048 bytes)

4. The additional information bytes. (0-7 bytes)

5. The time stamp indicating the time in the frame when the first byte(Circuit ID) of the Packet Header was received. (2 bytes)

Four registers are defined in the NI Base Register for the ProcessorData circular buffer. A diagram 800 of these registers can be found inFIG. 8. The Processor Data Start register contains the address of thefirst byte of the circular buffer. This register is written by theControl Processor 107 and read by the Network Interface 105. TheProcessor Data End register contains the address of the last byte of thecircular buffer. This register is also written by the Control Processorand read by the Network Interface.

There are two additional registers for the circular buffer. The first isthe Processor Data Read register. This register is used by the ControlProcessor to tell the Network Interface the address of the first byte ofthe next packet the Control Processor 107 will read. The ControlProcessor 107 only writes this register after it has read the completepacket. In other words, the Processor Data Read register will alwayspoint to the first byte of packet. The last register is the ProcessorData Write register. This register is used by the Network Interface topoint to the address that will be written into. It is written by theNetwork Interface 105 and read by the Control Processor 107.

The Network Interface 105 will check to determine if there is space inthe buffer to write a packet before it is written. If there is notenough space, the packet will not be stored.

Referring again to FIG. 5, the Control Buffer 509 provides storage forthe address/command bytes used to control the NI Data Bus 201. Theaddress of the Control Buffer is determined by the Control BufferAddress Register in the NI Base Registers. The buffer is loaded with theappropriate address/command bytes by the Control Processor 107. It isaccessed at the same rate as the clock for the output data on the NIData Bus 201. The buffer is reset to its starting location, the addresscontained in the Control Buffer Address Register, at the same time asthe Data Buffer is reset. This allows for synchronization between theControl and Data Buffers.

Referring still to FIG. 5, the last section of memory is the Data Buffer507. The buffer contains the same number of bits as the frame. For a1-millisecond frame at 40 Mbps, the Data Buffer contains 40,000 bits, or5,000 bytes. The address of the Data Buffer is determined by the DataBuffer Address Register in the NI Base Registers, and the size by DataBuffer Size Register.

Packets are written into the Data Buffer 507 by the Input block 405 orthe Control Processor 107. When a path (virtual circuit ID) isestablished, the Control Processor writes the packet header 315 into theData Buffer 507. The Input block 405 will only transfer the info field313 of the incoming packet 300. The Control Processor 107 writes theentire packet for control, casual, and LAN data.

The control processor 107 is responsible for initializing the NetworkInterface Base Registers, Virtual Circuit Registers, and the AddressRegisters. As routing changes, it has to update the Virtual CircuitRegisters. It is also responsible for writing the packet header into theData Buffer for all outgoing packets.

A set of registers is used to program the Network Interface 105. Theycontrol the addresses of the output buffer, address registers, andvirtual circuit registers, the synchronization of the frame, the size ofthe output buffer, the speed of the output clock, and interrupts. TheNetwork Interface Base Registers consist of twelve consecutive 16-bitregisters located at hex addresses FCOO through FC!7 in the NI memoryspace, but are not contained in the NI Memory. A diagram 800 of theregisters is shown in FIG. 8.

The Status/Control Register 900 is shown in FIG. 9. The Status/ControlRegister 900 is used to enable interrupts and also to identify what typeof interrupt has occurred. The register is read/write and is bits 0through 7 of the first NI Base Register.

Referring now to FIG. 9, it is seen that bit 6 is used to enable thePacket Received interrupt 901. If bit 6 is set to a 1, an interrupt willoccur when a packet is received and the Signal CP bit is set in theVirtual Circuit Register. Bit 7 is set to 1 when the entire packet hasbeen received and the Signal CP bit is set in the Virtual CircuitRegister. Bit 7 in the Status/Control Register 900 is cleared afterbeing read by the CP.

Bit 4 is used to enable the Start of Frame interrupt. If bit 4 is set toa 1, an interrupt will occur when the NI 105 reaches the beginning ofthe frame. Bit 5 will be set to a 1 to indicate that the interrupt wascaused by a Start of Frame. Bit 5 in the Status/Control Register 900 iscleared after being read by the CP.

Both the Packet Received and Start of Frame interrupts will be the sameinterrupt level to the Control Processor. The CP will have to read theStatus/Control Register 900 to determine which caused the interrupt.

Bit 1 in the Status/Control Register 900 is used to reset the NetworkInterface 105. This is the same as a power-up reset. The end result ofan NI reset is to guarantee the Control Bus 203 will not output anyaddresses. The NI can also be reset via a Reset Line from the ControlProcessor 107.

The CP writes a one to bit 0 in the Status/Control Register 900. Thiscauses the NI 105 to reset and disable the Control Bus 203. The ControlBus 203 remains disabled until the CP 107 writes a zero to bit 0 in theStatus/Control Register 900.

The Clock Divisor Register determines the bit rate of the output of theNetwork Interface 105. Bits 0 through 7 of the second NI Base Registercontains the divisor of the output clock. The register is read/write.The Clock Divisor can be any value between 00000000 and 11111111. Table1 contains preferred values for the clock divisor and the correspondingbit rate.

                  TABLE 1    ______________________________________    Typical Clock Divisors    Clock Divisor    Value                Bit Rate    ______________________________________    00000001             40 Mbps    00000010             20 Mbps    00000100             10 Mbps    00001000             5 Mbps    00010000             2.5 Mbps    00100000             1.25 Mbps    ______________________________________

The Sync Offset Register is used to synchronize the Data and ControlBuffers to the system frame. Bits 0 through 12 of the third NI BaseRegister contain the Sync Offset and are read/write. A Frame Sync packetcontains the position of the packet in the frame. When the packet 300 isreceived, the position in the Data Buffer 507 is stored with the packet.The Control Processor 107 compares the two values to determine if theData Buffer is in sync with the frame. If not, the Control Processor 107loads an offset value into the Sync Offset Register. This register isused to load the Data Buffer Counter at the end of the Data Buffer 507.After the Sync Offset Register is loaded into the Data Buffer Counter,it is cleared by the Network Interface.

The Data Buffer Size Register sets the size of the Data Buffer in bytes.Bits 0 through 12 of the fourth NI Base Register contain the Data BufferSize and are read/write. The Data Buffer Size, in conjunction with theClock Divisor, determines the length of the frame. Table 2 shows thepreferred Output Buffer size for allowable frame sizes as a function ofbit rate. The Data Buffer can be any size, and the maximum is determinedby the available NI memory.

The Data Buffer Size is used to determine the end of the frame. Thecounter that is used to sequence through the Data Buffer is compared tothe Data Buffer Size. When the counts are equal, the counter is loadedwith the value in the Sync Offset Register, the Data Buffer Address isloaded into the counter used to address the Data Buffer, and the ControlBuffer Address is loaded into the counter used to address the ControlBuffer.

                  TABLE 2    ______________________________________    Typical Data Buffer Size (bytes)               Frame Length (ms)    Mbps      1             2      4    ______________________________________    40        5000    20        2500          5000    10        1250          2500   5000    5         625           1250   2500    2.5                     625    1250    1.25                           625    ______________________________________

The Control Buffer Address Register defines the starting location in theNetwork Interface memory of the Control Buffer. It is the fifth NI BaseRegister and is read/write. The Control Buffer Address Register is usedto change Control Buffers.

The Data Buffer Address Register defines the starting location in theNetwork Interface memory of the Data Buffer. It is the sixth NI BaseRegister and is read/write. The Data Buffer Address Register is used tochange Data Buffers. This register is used in conjunction with theVirtual Circuit Pointer Register to change the structure of the frame.

The Virtual Circuit Register Pointer defines the upper portion of theaddress for the Virtual Circuit Registers. It is bits 11 through 15 ofthe seventh NI Base Register and is read/write. It provides bits 11through 15 of the address for the Virtual Circuit Registers' area ofmemory in the Network Interface memory. Bits 3 through 10 are providedby the Virtual Circuit ID in the incoming packet.

The Address Register Pointer defines the upper portion of the addressfor the Address Registers. It is bits 8 through 15 of the eighth NI BaseRegister and is read/write. It provides bits 8 through 15 of the addressfor the Address Registers' area of memory in the Network Interfacememory. Bits 4 through 7 are provided by the Address Type field, andbits 0 through 3 are generated based on the value of the Address Lengthfield in the incoming packet header.

The Processor Data Buffer Start register defines the start of thesection of NI Memory that is used to store data that is destined for theControl Processor. It is bits 0 through 15 of the ninth NI Base Registerand is read/write. The Processor Data area of NI Memory is a circularbuffer, and this register defines the top of the buffer.

The Processor Data Buffer End register defines the end of the section ofNI Memory that is used to store data that is destined for the ControlProcessor. It is bits 0 through 15 of the tenth NI Base Register and isread/write. The Processor Data area of NI Memory is a circular buffer,and this register defines the bottom of the buffer.

The Processor Data Read Pointer register defines the address of the nextpacket in the Processor Data area of NI Memory to be read by the ControlProcessor. It is bits 0 through 15 of the eleventh NI Base Register andis read/write. The Control Processor will write this address only afterthe packet has been completely read out of NI Memory. After a completepacket is read, the CP will write the address of the next packet intothe Processor Data Read register. The address contained in the ProcessorData Read register will always address the beginning of a packet in NIMemory.

The Processor Data Write Pointer register defines the next address inthe Processor Data area of memory that will be written into by theNetwork Interface. It is bits 0 through 15 of the twelfth NI BaseRegister and is read only. The Network Interface updates this registeras packets are written into the Processor Data area of NI Memory. The NIwill check this register against the Processor Data Read Pointerregister to prevent the information from being overwritten.

The parameters of the Virtual Circuit are contained in the VirtualCircuit Registers in the Network Interface Memory. There is a bank of256 Virtual Circuit Registers arranged consecutively in memory addressedby a pointer in the NI Base Registers. The contents of the registers areshown in FIG. 9. The registers are used by the Circuit ID field of anincoming packet to determine where in memory the packet is to be stored,the maximum allowable packet length, how many bytes will be sent afterthe end of the packet, if the packet is destined for the ControlProcessor, and if the Control Processor is to be interrupted. There area total of 256 Circuit IDs; some are reserved for special packets suchas reset, frame sync, and control data. The Circuit ID contained in thepacket is an offset to the address of the proper Virtual CircuitRegister.

Referring now to FIG. 10, the Destination Address in the Virtual CircuitRegister 1000 defines where in the Network Interface memory 111 the Infofield 313 of incoming packet 300 will be stored. It is the first word inthe Virtual Circuit Register 1000. The Destination Address is theaddress in NI memory 111 of the start of the storage area for a packetwith a given Virtual Circuit ID.

The Maximum Packet Size field identifies the largest packet that will betransferred for a given Virtual Circuit ID. It is contained in bits 0through 15 of the second word of the Virtual Circuit Register 1000. TheMaximum Packet Size is used as a safeguard to keep a packet 300 fromoverwriting memory. If the Packet Length 303 is greater than the MaximumPacket Size, the Info field 313 of the packet 300 will not be stored,and the Network Interface will generate a Packet End signal 421. See thetiming diagrams in FIGS. 11-17.

In order to keep an invalid Virtual Circuit ID from overwriting memory,the Maximum Packet Size for all unused Circuit IDs should be set to zeroby the Control Processor 107.

The Additional Bytes Expected field defines the number of bytes thatwill follow the end of the information field 313 of the packet 300. Itis contained in bits 0 through 2 of the third word of the VirtualCircuit Register 1000.

There can be zero to seven bytes following the info field 313. Thisinformation is sent immediately following the end of the packet 300. TheNI-Bus 101 devices start sending the bytes, if any, after the Packet Endline 421 goes from low to high. Packet End 421 will remain high untilall additional bytes have been received or Packet Start 417 goes low.The device has to still generate the Data Clock signal 419 for each ofthe additional bytes. See the timing diagrams in FIGS. 11-17.

The Signal CP Flag is used to determine if a packet for a given VirtualCircuit ID should generate a signal to the processor 107. This is usefulif the packet is being written into the Processor area of the NetworkInterface Memory 111. The flag is bit 3 of the third word of the VirtualCircuit Register 1000. If this bit is 1, bit 7 (901) of theStatus/Control Register 900 will be set to a 1 when a packet is writteninto the processor area of the NI Memory 111. If bit 6 (903) of theStatus/Control Register 900 is set to a 1, an interrupt will begenerated to the Control Processor 107.

The CP Data Flag indicates if a packet with this Circuit ID is destinedfor the Control Processor 107. If the flag is One, the Info field 313 ofthe packet 300 will be written into the Processor area of the NI Memory111, and the address contained in the Destination Address will beignored. The flag is bit 4 of the third word of the Virtual CircuitRegister 1000.

The Encryption Type field defines the type of encryption to be used fora given Virtual Circuit. The field is bits 5 and 6 of the third word inthe Virtual Circuit Registers. Currently, the only encryption type thatis defined is 00, which is no encryption. For the prototype, the NetworkInterface 105 will not be required to do anything with these bits.

The Network Interface Bus 101 (NI-Bus) Signals are described below.

The Data Bus 201 comprises 8 lines designated NDO through ND7.--These 8three-state, bi-directional lines are the path for transferring databetween the Network Interface 105 and peripheral devices connected tothe NI-Bus 101.

The Control Bus 203 comprises 8 lines designated NC0 through NC7--These8 three-state output lines are for addressing/commanding devicesconnected to the NI-Bus 101.

The Control Clock (CCLK) line 427's output signal, when high, indicatesthat there is valid Control information on the Control Bus 203.

The Data Clock (DCLK) line 419's signal, when high, indicates that thereis valid data on the NI Data Bus 201. The device driving the NI Data Bus201 is responsible for driving this signal.

The Packet Start (PS) 417's input signal goes high and remains highwhile data is being sent from a peripheral device. The signal 417 willgo low after Packet End 421 signal goes low. The device driving the DataBus 201 drives the Packet Start signal 417.

The Packet End (PE) 421's output signal goes high to inform theperipheral device that all valid packet data has been received and thatextra data bytes, if any exist, may be transmitted. The signal 421 goeslow when all additional bytes have been received. The signal will gohigh if a Max Packet Size or CRC error occurs.

The Timing Specification is described as follows:

Refer to FIGS. 11-17.

FIG. 11 shows the network interface control transfer timing.

FIG. 12 shows the timing for a data transfer from a device to thenetwork interface with no additional bytes.

FIG. 13 shows the timing for a data transfer from a device to thenetwork interface with additional bytes.

FIG. 14 shows the timing for a data transfer from the network interfaceto a device.

FIG. 15 shows the timing for a data transfer from a device to thenetwork interface with a maximum packet size error or a space availableerror.

FIG. 16 shows the timing for a data transfer from a device to thenetwork interface with a CRC error.

FIG. 17 shows the timing for a data transfer from a device to thenetwork interface with an address error.

The maximum rise and fall times for CCLK 427, DCLK 419, PS 417, and PE421 are 5 nanoseconds. Rise and fall times are from 10% to 90%. Alltimes are typical unless otherwise noted.

FIG. 18 illustrates a typical format for information being sent duringone time slot on a packet bus. The format illustrates the transmissionof local bus control information, packet preamble information, a packetheader, and packet information (message data). The bus controlinformation consists of the address of one of the interfaces coupled tothe packet bus. The packet preamble is provided for synchronizationpurposes. The packet header will be explained in more detail below. Thepacket information represents the information to be communicated betweenusers.

FIG. 19 illustrates information contained within the packet header asshown in FIG. 18 in accord with the present invention. The headerincludes a virtual circuit identification, packet length information,ultimate destination information, and validation information. Thevirtual circuit identification contains information that specifies avirtual circuit register contained within the network interface. Furtherinformation on this element is provided with regard to the followingfigures. The packet length provides information concerning the length ofthe associated packet. The destination information may include bothdestination and originating address information. The validationinformation contains data associated with a CRC data accuracycalculation.

FIG. 20 illustrates an exemplary packet handling and organization methodaccording to the present invention. In the illustrative embodiment ofthe present invention, the packet information as identified in FIG. 18is stored in buffers 52A-52C and 54A-54C. These buffers constitutesections of the data memory portion of memory 111. The control memoryportion of memory 111 provides storage for the commands associated withthe other elements shown in FIG. 20. These elements facilitate a methodfor organizing and reorganizing packets according to a hierarchicalapproach.

Virtual circuit register 42 points to or addresses a queue control block44. Each queue control block can point to a write packet descriptor or aread packet descriptor. As illustrated, queue control block 44 points topacket descriptor 46A.

Each packet descriptor can point to a write buffer descriptor and a readbuffer descriptor. In addition, it can point to one other packetdescriptor. As illustrated, packet descriptor 46A points to bufferdescriptor 48A and to packet descriptor 46N.

The buffer descriptors each point to one buffer and to a next writebuffer descriptor and a next read buffer descriptor. In the illustrativeembodiment, buffer descriptor 48A-48C point respectively to buffers52A-52C. Also the buffer descriptor 48A points to buffer descriptor 48Bwhich in turn points to buffer descriptor 48C thereby forming acontinuous chain or link. Buffer descriptors 50A-50C are likewiseorganized with regard to each other and buffers 54A-54C.

Before further explaining the functioning of these elements it isbelieved that an explanation of the benefits of this organization willassist in comprehending the organization and function of each element.An important aspect of this invention is to provide an improved level offlexibility in defining and redefining a packet without requiringsubstantial data duplication by a microprocessor. This is generallyaccomplished by providing a hierarchy of addressability wherein receivedpackets are disassembled and stored in segregated memory locations.Packets to be transmitted are assembled by sequentially addressing thesegregated memory locations.

FIG. 21 illustrates an exemplary embodiment of the contents of a virtualcircuit register 42. As illustrated, it includes a queue control blockaddress 56, maximum packet size information 58, virtual circuit typeidentifier 60, a central processor (CP) send interrupt data 62, CPreceive interrupt data 64, and miscellaneous control data 66. Address 56is utilized to point to the queue control block 44. The maximum packetsize field identifies the largest packet that can be received for agiven virtual circuit register. This can be utilized as a safeguard tokeep a packet from over-writing memory. The virtual circuit type dataindicates if the particular virtual circuit register is valid as aninput or output circuit. The CP send and received interrupt fieldsdetermine if a CP interrupt is to be generated and if so, its priority.The miscellaneous control data field can be utilized to accommodateadditional control information which may be useful for a specificimplementation of a method in accordance with the present invention.

FIG. 22 illustrates the fields associated with a queue control block 44.The queue control block consists of write and read packet descriptoraddress 68 and 70, respectively. The write packet descriptor addresspoints to the packet descriptor to be used in writing a received packet.The read packet descriptor address points to the packet descriptor to beused in reading a packet to be transmitted. These addresses are updatedas packets are received and transmitted.

FIG. 23 illustrates the fields associated with packet descriptors 46.Each packet has one assigned packet descriptor that points to read andwrite buffer descriptors. The write buffer descriptor address 72 pointsto the first buffer descriptor to be used for receiving a packet. Theread buffer descriptor address 74 points to the first buffer descriptorto be used for sending a packet. The next packet descriptor address 76is used to point to the next packet descriptor in ring 77 (see FIG. 20).In the illustrated embodiment, packet descriptors 46A through 46N form aring in which each points to the next, and wherein the last packetdescriptor 46N points to the first or beginning packet descriptor 46A.It should also be noted that the packet descriptors are capable ofpointing to any packet descriptor not merely the next adjacent packetdescriptor in memory. Further, the ring could consist of but a singlepacket descriptor in which its next packet descriptor address points toits own address. The frame number field 78 indicates in which frame thepacket was received. The frame position field 80 indicates the positionin the frame of the start of the packet preamble. The miscellaneouscontrol data field 82 can be utilized to store desirable data associatedwith the packet descriptor level to accommodate specificimplementations.

FIG. 24 illustrates the fields constituting a buffer descriptor. Thebuffer address field 84 contains the address of the first byte in thebuffer pointed to by the buffer descriptor. In the illustrated example,buffer descriptor 48A would contain a buffer address pointing to thefirst byte contained in buffer 52A. The next write buffer descriptoraddress field 86 is used to point to the next buffer descriptor to beused for writing a packet. Similarly, the next read buffer descriptoraddress field 88 is used to point to the next buffer descriptor to beused for reading a packet. The amount of data field 90 indicates theamount of the buffer that has been used. The buffer sized field 92indicates the absolute size of the buffer. The miscellaneous controldata field 94 may contain useful data associated with the the bufferdescriptor level for a particular implementation. For example, themiscellaneous data field 94 may contain a flag which indicates the endof a packet.

The central processor is responsible for managing the virtual circuitregisters, queue control blocks, packet descriptors, buffer descriptorsand buffers. It will be apparent to those skilled in the art that thereare many methods by which the central processor can manage the fieldsand memory associated with this organizational hierarchy for receiving,storing and retransmitting a packet. For example, the queue controlblock could be used to point to a fixed set of packet descriptors whichin turn point to a fixed set of buffer descriptors. To add or deletepackets from a queue, the write buffer descriptor address 72 (if packetsare being received) or the read buffer descriptor address 74 (if packetsare being transmitted) could be changed.

In another method, each packet could have a dedicated set of bufferdescriptors which in turn has a dedicated packet descriptor. To add ordelete packets from a queue, packet descriptors could be added ordeleted from a packet descriptor ring by changing the next packetdescriptor address 76 to point to packet descriptors in a desiredsequence. These methods are illustrative only and indicate the greatdegree of flexibility with which the designer can control packettransmission in accordance with the method of the present invention.

Some of the further advantages of the method according to this inventionare discussed as follows. Although the virtual circuit registers musteach point to only one queue control block, a plurality of virtualcircuit registers can point to the same queue control block. This may bedesirable where a plurality of packets which are identical or containsubstantial similarities are encountered. Differences between thepackets could be stored in different buffers and the common contents ofthe packets stored in a common set of buffers. The CP could change thenext read buffer descriptor addresses 88 accordingly to point to theproper sequence of buffers for the slightly different packets.

The read and write addresses in the queue control block allows the samevirtual circuit register to be able to receive and transmit a packet.This conserves the number of virtual circuit registers required andminimizes repetitive data transfer between receive and transmit cycles.

Each packet descriptor defines a particular packet. An important aspectof the packet descriptors is the ability to point to a next packetdescriptor via address 76 to form a circular ring of packet descriptorswhich point respectively to multiple packets. The size of the ring, i.e.the number of packets which can be consecutively identified, is limitedonly by the ultimate memory capacity available in the control memory anddata memory. Since everything below the packet descriptor level isrelevant to only one packet, the CP does not have to move redundant datain order to be able to retransmit the packet. This provides asubstantial advantage especially when utilized in a packet repeater inwhich many if not all of the received packets must be retransmitted.

The buffer descriptors permit a plurality of fixed size buffers to beeconomically utilized. Since a plurality of buffers can be linked bymeans of the buffer descriptors, this permits common or repetitiveinformation or control data to be stored in selected buffers andincorporated when needed by addressing the associated buffer descriptorand changing its next (write or read) buffer descriptor address asrequired. For example, a commonly used packet preamble consisting ofsynchronization data could be stored in one buffer or if too large forone buffer a series of linked buffers by associated buffer descriptorswhereby the first associated buffer descriptor can be addressed and thenext (write or read) buffer descriptor addressed changed for each newpacket to be transmitted. This also provides the advantage ofpermanently storing certain information in buffers and allowing reuse ofthat information by directly reading it from the buffer at theappropriate sequence in later generated packets.

FIG. 25 illustrates a wireless TDMA packet network embodying the presentinvention. A control module (CM) 1812 functions as a master node andcommunicates using radio frequency signalling with user modules (UM)1814. Each UM is connected to one or more terminals 1816. Each terminalis representative of a communications device which utilizes digitalsignalling and may comprise a personal computer, computer peripherals,or video and audio equipment which converts images or sounds intodigital data. The CM 1812 is preferably connected to a network such asEthernet by a communication channel 1818 which may comprise coaxialcable or other means. In the illustrative embodiment, the CM and UM'scommunicate with each other using six directional antennas A1-A6oriented to cover 360° in the horizontal plane. Depending on thepositioning of the UMs relative to the CM, different antennas willlikely provide the best communications path. It should also be notedthat for such a network installed in a building, the directcommunication path may not always be available because of objects or maychange due to the movement of people. Thus, different antennacombinations will be utilized between a UM and the CM based on changesin the environment.

FIG. 26 illustrates a block diagram of a structure common to both the CMand UMs of FIG. 25. An RF transceiver 1820 utilizes digital data tomodulate an RF carrier to transmit the desired data and its receiverconverts received RF signals into corresponding digital data. Any one ofantennas A1-A6 can be coupled to the transceiver 1820 by antennaselector 1822 which may comprise a conventional mechanical or electronicswitching control. A microprocessor 1824 operates under the control ofan operating system contained in read only memory 1826 and utilizesrandom access memory 1828. The microprocessor 1824 controls inbound andoutbound data carried by path 1832, the transceiver 1820, and antennaselector 1822. An interface 1830 may consist of line drivers andinput/output buffers and registers as is conventional in microprocessorsystems. The path 1832 corresponds to communication channel 1818 wherethe embodiment is utilized as a CM and corresponds to the connection toa terminal where the embodiment is utilized as a UM. The microprocessoroperation relating to synchronization is explained below.

The use of different directional antennas complicates the problem ofmaintaining relative time synchronization between each of the UMs andthe CM. Since the UMs and CM each communicate using only one selectedantenna at any given time, it cannot be assumed that each UM willreceive synchronization signals or information transmitted by the CMusing a particular CM antenna.

It is important that the UMs each remain in time synchronizationrelative to the CM so that each UM can receive transmissions addressedto it during a predetermined time slot in a frame and transmitinformation to the CM at a predetermined time slot. The lack ofsynchronization would result in multiple signal collisions and aresulting loss of data.

FIG. 27 illustrates a flow diagram utilized by the CM to generate framesynchronization packets that are transmitted over each CM antenna. Step1834 represents a byte counter implemented in the microprocessor systemwhich maintains a running count N of the number of bytes generated sincethe beginning of a frame. In step 1836 a decision is made as to whetherthe byte count N is equal to a predetermined frame sync number FScorresponding to the byte position relative to the start of the frame atwhich frame sync packets are transmitted by the CM. A NO determinationresults in returning to the byte counter and waiting until the FS byteis reached. Upon a YES determination, step 1838 makes the decision as towhether a frame count (FC) is even. The microprocessor contains a framecount register maintaining even/odd determination of consecutivenumbered frames. A NO determination, corresponding to the frame countbeing odd, results in the transmission of frame sync packets overantennas A1, A3, and A5 by step 1840. A YES determination results inframe sync packets being transmitted over antennas A2, A4, and A6 bystep 1842. Following the transmission of the frame syncs packets, thismethod ends at END 1844.

The CM does not transmit a frame sync packet over each antenna duringeach frame. In illustrative embodiment, half the frame synchronizationpackets are transmitted every other frame. This permits each frame toutilize three additional time slots for information or other purposesthat would have otherwise been utilized if a frame sync packet wastransmitted over each antenna during every frame. While one CM antennawill be preferable to the others for communications with a UM, it islikely that a UM may be able to receive signal transmissions over CMantennas adjacent the most preferred antenna. By selecting three CMantennas with maximum spacings (every other antenna) for thetransmission of frame sync packets during each frame, it is likely thatany given UM will be able to receive one of the frame sync packets. EachUM should receive a frame sync packet at least every other frame sinceit will be transmitted by the most favored CM antenna.

FIG. 28A illustrates the format of a frame sync packet 1846 as containedwithin a frame 1848 transmitted by the CM as shown in FIG. 28B. Thesynchronization packet 1846 preferably contains a header 1850,miscellaneous information and data 1852, the frame number 1854, theframe position 1856, and a cyclic redundancy calculation 1858 used forerror checking. The frame position 1856 contains the frame position inbytes relative to the CM frame start 1862. The time stamp (TX₋₋TIMESTAMP 1860) defined by the bytes in frame position 1856 actuallyreflects a time X bytes after the start of the packet 1846 since Y bytesof buffering are utilized prior to the actual transmission of each byte,i.e. Y bytes are prefetched in preparation for transmission of eachbyte. It is common in most systems for data to be retrieved andassembled a predetermined time before transmission.

In FIG. 28B, the CM frame 1848 illustrates three frame synchronizationtime slots 1864, 1866, and 1868. The remaining portion of the frame isdivided into a plurality of time slots utilized for the transmission ofinformation and data between the UMs and the CM. The frame startposition 1862 marks the beginning of the frame having a predeterminedtime T which corresponds to a predetermined number of bytes B. Threeframe sync packets are transmitted at these predetermined time slotsrelative to frame start 1862. In the illustrative embodiment, theseframe sync packets will be transmitted by antennas A1, A3, and A5,respectively during an odd frame and during even frames these packetswill be transmitted by antennas A2, A4, and A6 respectively.

FIG. 28C illustrates a UM frame 1870 having a frame start reference 1872and including frame sync time slots 1874, 1876, and 1878 reserved forthe reception of the frame sync packets. Frame 1870 is divided into aplurality of time slots corresponding to the same time slots defined bythe CM frame 1848. A time stamp is provided at the reception of thefirst byte of each of the frame sync time packets. An RX₋₋ TIMESTAMP1880 corresponds to the frame position in bytes relative to frame start1872 when the first byte of the frame sync packet for slot 1878 wasreceived. In the illustrative example it is assumed that frame syncpacket 1846 transmitted in slot 1868 is received in slot 1878 and thatframe sync packets transmitted in corresponding time slots 1874 and 1876are not received. Because of inherent time delays introduced by the CMtransmitter and the UM receiver, Z bytes of delay exist between thestart time of slots 1868 and 1878 as shown in FIG. 28C.

FIG. 29 illustrates a flow diagram by which each UM generates a framestart interrupt. In step 1882, the current byte count M relative to thebeginning of a UM frame is maintained. In decision step 1884, adetermination is made if the current byte count M=FE (frame end). A NOdecision returns to step 1882 to await another byte count increment. AYES decision causes step 1886 to generate a frame start interrupt whichmarks the end of a preceding frame and the beginning of a new frame.

FIG. 30 is a flow diagram of steps taken by the UM to determinesynchronization relative to the CM. In step 1888 the UM waits for twoframe start interrupts to have occurred. Since the CM transmits a framesync packet on each antenna during a two frame cycle, this waiting timeallows the UM to attempt reception of each sync packet. In step 1890 adetermination is made if a frame sync packet has been received. A NOdetermination causes step 1892 to change to a different UM antenna andreturn to step 1888 for the possible reception of a sync packet usingthe different receiving antenna. A YES determination by step 1890results in step 1894 storing the frame position in bytes at the UM framewhen the first byte of a frame sync packet arrives. This positioncorresponds to RX₋₋ TIMESTAMP 1880. In step 1896 the frame positioncontained in the frame sync packet, TX₋₋ TIMESTAMP, is read. In step1898 a calculation is made to determine the OFFSET, if any, of the UMframe relative to the CM frame. In this calculation, OFFSET=TX₋₋TIMESTAMP minus RX₋₋ TIMESTAMP plus CONSTANT. The CONSTANT is thedifference between RX₋₋ TIMESTAMP and TX₋₋ TIMESTAMP when the CM and UMframes are in perfect time synchronization. The CONSTANT (delay value)consists of the number of bytes of delay introduced by the CMtransmitter and UM receiver minus the X byte difference in the recordingof the TX₋₋ TIMESTAMP relative to the RX₋₋ TIMESTAMP. In step 1900 thedetermination is made if OFFSET=zero. If YES (no adjustment to UMsynchronization is needed), the UM antenna is changed at step 1892 andcontrol passes to step 1888. A NO determination (a synchronizationadjustment is required), results in step 1902 writing the OFFSET valueinto a frame position OFFSET register contained in interface 1830 in theUM. Following step 1902, step 1892 is executed and the cycle returns tobeginning step 1888. Thus, the UM makes a synchronization adjustmentdetermination and provides the compensation value OFFSET in a registerwhich is utilized as will be explained in regard to FIG. 31. It shouldbe noted that step 1892 could be skipped following steps 1900 and 1902since a frame sync packet was received. However, the UM antenna ischanged in the preferred embodiment after each cycle shown in FIG. 30 topermit an antenna evaluation algorithm to continuously evaluate the bestUM antenna for communication with the CM.

FIG. 31 illustrates the steps in a method implemented by themicroprocessor of the UM. In step 1904 the UM waits for a frame startinterrupt generated by step 1886. Upon receiving the frame startinterrupt, step 1906 causes the frame position offset register to beread. In step 1908, the frame position offset register is reset to zero.In step 1910 a determination is made if the offset is equal to zero,i.e. the value which was written into the frame offset register. A YESdetermination results in step 1912 causing the new UM frame to start theframe position with a zero byte count in the offset register, i.e. noshift, and a return to step 1904. A NO determination results in step1914 making a further determination as to whether OFFSET was greaterthan zero. A YES determination results in step 1916 causing the UM bytecount to start with a frame position equal to OFFSET, i.e. the new framestarts from a count equal to OFFSET which will have the effect ofadvancing the UM frame in time relative to the CM frame. Following step1916, a return is made to step 1904. A NO determination by step 1914(which corresponds to offset having a negative integer value), resultsin step 1918 causing the UM frame byte counter to count from offset upto zero. This has the effect of delaying the UM frame relative to the CMframe. Following this additional delay, the frame continues at the zerobyte count and counts towards the predetermined number of bytescontained within a normal UM frame by step 1912. Thus, the UM frame isadjusted in time relative to the CM frame.

In the preferred embodiment of the invention, each CM and UM framecontains a first time slot having a predetermined number of expendablebytes which are not allocated for data or message information. Thisenables these bytes at the beginning of the frame to be lost without theloss of frame information when the UM frame count starts at a numbergreater than zero. The number of expendable bytes is preferably setlarge enough to accommodate the typical positive offsets which may beutilized in maintaining synchronization.

It will be apparent to those having ordinary skill in the art that theCM and each UM will contain an independent clock oscillator such ascontrolled by a crystal for generating timing. Therefore, the rate offrequency (time) change between clocks in the CM and each UM willnormally be small and will result in the UMs requiring OFFSET adjustmentby only one byte once in a substantial number of frames. Thus, even if aframe sync packet is not received for several frames, synchronizationwill not be lost.

An advantage of the synchronization method and apparatus according tothe present invention resides in the distributed nature of theadjustments in which each UM is free to make an independent adjustmentrelative to the CM. Not only does this maintain system synchronizationof the UMs relative to each other, but it also relieves the CM of thetask of calculating synchronization adjustments for the different UMs.

Another advantage of the present invention is that additional time slotsare available in each frame which would have been occupied by frame syncpackets if a sync packet was transmitted on each antenna during eachframe. Instead of transmitting three sync packets each frame, two syncpackets could be transmitted each frame thereby requiring a total ofthree frames to complete the transmission over each antenna. In thiscase sync packets would preferably be grouped corresponding to antennasA1, A4; A2, A5; A3, A6 so that at least one sync packet is transmittedin each 180° horizontal plane during each frame to enhance thepossibility that one will be received as soon as possible in the 3 framesequence.

FIG. 32 illustrates a wireless packet communication system in which acontrol module 2010 utilizes RF communications to communicate with usermodules 2012 that are each coupled to one or more user devices 2014consisting of a terminal, personal computer, telephone, or otherinformation input/output device. In the illustrative system, the controlmodule 2010 is also coupled by a data channel 2016 to a data network.The control module controls communications within the illustratednetwork and passes information from the data network via channel 2016 touser devices 2014 via the associated user module. The control modulealso controls local communications by receiving information from oneuser module and relaying the information to a different user module. Thewireless information is conveyed in the form of packets. The datanetwork to which control module 2010 is connected may consist of anEthernet network.

FIG. 33 illustrates a preferred embodiment of a packet format utilizedfor communications over the NI bus. It is segmented to contain a NIheader, a packet header, a data information portion, and a cyclicredundancy calculation field for error checking. The NI header includesa NI address, i.e. the address of a peripheral device connected to theNI bus, a field indicating the length of any NI information, and NIinformation which may consist of commands. The NI header is used by thecommunication controller in transmitting packets to the NI peripheraldevices. A NI header is not utilized when a peripheral device transmitspackets on the NI bus since all such packets are only received by thecommunication controller.

The methods described below will most advantageously be integrated intoa conventional software operating system that provides variousoperational capabilities dependent upon the specific operatingenvironment.

FIG. 34 is a flow diagram illustrating the steps implemented by thecommunications controller to transmit data or commands to a peripheralconnected to the NI bus. The timing diagram illustrated in FIG. 35 alsorelates to the transmission of packets of data from the communicationscontroller to the peripherals and should be read in conjunction with thesteps described in FIG. 34. The timing diagram in FIG. 35 represents thephysical NI bus which consists of a packet bus having a plurality oflines for conveying a byte of data during each bus clock cycle andseparate control lines for packet clock, packet start, NI source, andbus clock. The NI source and bus clock lines are always controlled bythe communications controller; the remaining lines and packet bus arebi-directional, i.e. the communications controller and the peripheralsare capable of writing to and reading these lines.

The transmission of data from the communications controller to aperipheral is accomplished as follows. Beginning with entry at START2052, the controller drives the NI source line from high to low asindicated in step 2054. This gives the controller control of the NI busand communicates to all peripherals that they are to receive data whichwill be transmitted from the controller. In step 2056 the controllerdrives the packet packet start line from high to low which marks thebeginning of the transmission of a packet to be transmitted by thecontroller to a peripheral. Next, the controller writes a byte of dataon the packet bus as indicated by step 2058. In step 2060, thecontroller drives the packet clock line from high to low and back high.The peripherals read the data written on the packet bus during the highto low transition of the packet clock. In decision step 2052 thecontroller determines if all data has been transmitted. If NO, the nextbyte of data is written on the packet bus by returning to step 2058 andthe cycle repeated. Upon completing the writing of all data (step2062=YES) the controller drives the NI source line from low to highreleasing control of the NI bus and packet start from low to highmarking the end of the packet in step 2064. This method terminates atEND 2066.

In the illustrative example as shown in FIGS. 34 and 35, thecommunications controller sent a single packet as illustrated in FIG. 33to one or a predetermined group of peripherals. The NI header containsthe peripheral address of a particular peripheral or a group address fora predetermined group of peripherals. After receiving and decoding theperipheral address contained in the NI header, each peripheral candetermine if the following information is intended for it. If theinformation is intended for a peripheral, then it will continue readingthe data transmitted by the controller. If the packet is not intendedfor a peripheral, then it need not further process the information andcan merely look for a low to high transition of the packet start lineindicating the end of transmission of that packet. Although theillustrative example indicated the simultaneous transition of NI sourceand packet start in step 2064, the controller may alternatively maintainthe NI source line low, indicate the end of the packet transmission bydriving the packet start line from low to high and then begintransmission of another packet by driving packet start from high to lowthereby not relinquishing control of the NI bus between the transmissionof successive packets. The packet clock line is controlled by thetransmitting device with the high to low transition being a signal tothe receiving device that data on the packet bus is stable and should beread.

FIG. 36 shows a flow diagram illustrating steps performed by aperipheral device in transmitting data to the communications controller.These steps should be read in conjunction with the timing diagram shownin FIG. 37. The timing diagram in FIG. 37 illustrates one additionalcontrol line, packet end, not shown in FIG. 35. In the precedingdescription relating to FIG. 35, the packet bus, packet clock, andpacket start lines were sourced by the communications controller Withregard to FIG. 37, the packet bus, packet clock, and packet start linesare sourced by a peripheral. The packet end, NI source, and bus clockare sourced by the controller.

In START step 2068, a flag (F) is set to zero. This flag generallyrelates to the ability of the controller to allow certain additionaldata to be transmitted after the end of the packet as marked by packetstart. The operation of this flag is explained in detail below. In step2070, a determination is made if packet start is high. A NO decisionresults in the termination of the method at END 2072 since packet startmust be high in order for a peripheral to initiate data transmission.Following a YES decision by step 2070, step 2074 determines if NI sourceis high. A NO decision by step 2074 results in a further decision bystep 76 in which a determination is made by the peripheral if it hasbeen instructed by a command from the controller on the packet bus totransmit data. A NO determination by step 2076 results in termination atEND 2072 since a peripheral will not normally be able to transmit datawhen the NI source line is low except upon being instructed by a priorcommand send by the controller on the packet bus. A YES decision by step2074 indicates that the NI bus is available for data transmission by theperipheral.

In step 2078 the peripheral drives packet start line from high to lowthereby advising the controller to receive data. The peripheral thenproceeds to write data on the packet bus in step 2080. The peripheralthen drives the packet clock line from high to low which provides atiming signal to the controller to read the data on the packet bus. Instep 2084 a decision is made if packet end is low. The packet end lineis controlled by the controller and is utilized to provide an overridecontrol which can be exercised by the controller to prematurelyterminate transmission by a peripheral. A NO decision in step 2084 leadsto a determination in step 2086 if flag F is high. A YES decisionresults in the peripheral initiating a stop sending data sequence 88 inwhich transmission of data is stopped. A NO determination by step 2086,i.e. the flag is not set, results in a determination by the peripheralas to whether all data has been transmitted in step 2090. A NO decisionreturns control to step 2080 in which additional data is transmitted tothe controller. A YES determination by step 2090, indicating the end ofdesired data transmission by the peripheral, results in step 2074determines if NI source is high. A NO decision by step 2074 results in afurther decision by step 2076 in which a determination is made by theperipheral if it has been instructed by a command from the controller onthe packet bus to transmit data. A NO determination by step 2076 resultsin termination at END 2072 since a peripheral will not normally be ableto transmit data when the NI source line is low except upon beinginstructed by a prior command send by the controller on the packet bus.A YES decision by step 2074 indicates that the NI bus is available fordata transmission by the peripheral.

In step 2078 the peripheral drives packet start line from high to lowthereby advising the controller to receive data. The peripheral thenproceeds to write data on the packet bus in step 2080. The peripheralthen drives the packet clock line from high to low which provides atiming signal to the controller to read the data on the packet bus. Instep 2084 a decision is made if packet end is low. The packet end lineis controlled by the controller and is utilized to provide an overridecontrol which can be exercised by the controller to prematurelyterminate transmission by a peripheral. A NO decision in step 2084 leadsto a determination in step 2086 if flag F is high. A YES decisionresults in the peripheral initiating a stop sending data sequence 2088in which transmission of data is stopped. A NO determination by step2086, i.e. the flag is not set, results in a determination by theperipheral as to whether all data has been transmitted in step 2090. ANO decision returns control to step 2080 in which additional data istransmitted to the controller. A YES determination by step 2090,indicating the end of desired data transmission by the peripheral,results in the peripheral driving the packet start from low to high asindicated in step 2092. This tells the controller that the peripheralhas finished transmitting the packet. Following step 2092 the methodterminates at END 2094.

The following explanation indicates the ability of the controller toprematurely end the transmission of data by the peripheral. Thissequence is initiated by the controller driving packet end line low, aYES decision by step 2084. In step 2096 the peripheral responds to thiscommand by setting flag equal to 1. In step 2098 a determination is madeby the peripheral if more data remains to be sent to the controller. ANO decision results in terminating the transmission by return to steps2092 and 2094. A YES determination by step 2098, indicating that moredata is to be sent, causes a return to step 2080 in which the next byteof data is written to the packet bus and the packet clock is incrementedin step 2082. If the packet end line remains low as determined by step2084 the same sequence of steps will proceed until the peripheral hastransmitted all of its data as determined by step 2098. However, if thecontroller has caused the flag F to be reset by driving packet end fromlow to high, a NO determination will be made by step 2084. In this case,step 2086 will result in a YES determination since the flag has been setthereby implementing the immediate stop function by step 2088. Thus, thecontroller can terminate the transmission of data by a peripheral bydriving packet end from high to low to high.

In the illustrative example as shown in FIG. 37, the packet start lineis driven by the peripheral from low to high prior to a packet end linetermination command, i.e. from high to low to high. Thus, this exampleillustrates that the peripheral completed the transmission of its datawithout a premature interruption by the controller. The heavy dashedline associated with the packet start line in FIG. 37 illustrates analternative example in which the peripheral continued to have data tosend but was interrupted by the packet end command, whereby the packetstart line remains low until the beginning of the heavy dashed line andreturns high concurrent with the packet end line being driven from lowto high by the controller. This mechanism is advantageous in that itpermits the possibility of additional bytes of data to be transmittedbeyond a predefined packet as determined by the packet start line. Thusit is possible for a peripheral to immediately send a number of bytes ofadditional information following a packet. Such bytes of information canbe utilized to monitor conditions of the peripheral or may correspond togeneral update information provided by the peripheral following thetransmission of the packet. This permits such information to becommunicated without requiring it being carried within a packet. Thisprovides additional flexibility of communications which is especiallyadvantageous when a plurality of peripherals each communicate with acommon controller.

If one peripheral is transmitting a packet of information which isdestined for another peripheral attached to the NI bus, the controllerwill process the packet and reformat a packet with a NI header addressedto the destination peripheral and transmit it over the NI bus. Thus, thecommunications controller acts as a traffic cop in routing packets andinformation between peripherals as well as providing a common point ofcoordination of communications.

While various embodiments of the invention have been described and shownherein, the scope of the invention is defined by the following claims.

We claim:
 1. A method for a device connected to a NI (network interface)bus having a packet bus and control lines to transmit data to acommunication controller connected to the NI bus comprising the stepsof:(a) determining if the NI bus is available to accept data from thedevice by determining if a first control line and a second control linehave a predetermined binary state; (b) if the NI bus is available toaccept data, the device causing the first control line to change to theother binary state; (c) writing a byte of data to be transmitted on thepacket bus; (d) causing a third control line that functions as a packetclock to change binary states thereby providing the communicationcontroller with a signal to read the written data; (e) if additionaldata is to be transmitted, repeating steps (c) and (d); and (f) causingthe first control line to change from the other state to thepredetermined state thereby indicating an end of data transmission. 2.The method according to claim 1 further comprising the steps ofmonitoring the binary state of a fourth control line under the controlof the communication controller and terminating the sending ofadditional data upon said monitoring step sensing a transition of thefourth control line from one state to the other state and back to theone state.
 3. The method according to claim 2 wherein said terminatingstep allows additional data to be transmitted until said fourth controlline changes from said other state back to the one state.
 4. A deviceconnected to a NI (network interface) bus having a packet bus andcontrol lines capable of transmitting data to a communication controllerconnected to the NI bus, said device comprising:means for determining ifthe NI bus is available to accept data from said device by determiningif a first control line and a second control line have a predeterminedbinary state; means for causing the first control line to change to theother binary state if the NI bus is available to accept data; means forwriting data to be transmitted on the packet bus; means for causing athird control line that functions as a packet clock to change binarystates thereby providing the communication controller with a signal toread the written data; means for determining if additional data is to betransmitted and causing said writing means and said third control linemeans to respectively, write the additional data on the packet bus andprovide the communication controller with a signal to read theadditional data; and means for causing the first control line to changefrom the other state to the predetermined state thereby indicating anend of data transmission.
 5. The device according to claim 4 furthercomprising means for monitoring the binary state of a fourth controlline that is under the control of the communication controller andterminating the sending of additional data upon said monitoring meanssensing a transition of the fourth control line from one state to theother state and back to the one state.
 6. The device according to claim5 wherein said terminating means allows additional data to betransmitted until said fourth control line changes from said other stateback to the one state.
 7. A method for a communication controllerconnected to a NI (network interface) bus having a packet bus andcontrol lines to transmit data packets to a device connected to the NIbus comprising the steps of:(a) obtaining control of the NI bus bycausing a first control line to change from a first binary state to theother binary state; (b) marking the beginning of a data packet bycausing a second control line to change from a first binary state to theother binary state; (c) writing a byte of data packet information to betransmitted on the packet bus; (d) causing a third control line thatfunctions as a packet clock to change binary states thereby providingsaid device with a signal to read the byte of data packet information;(e) if additional data packet information comprising the data packet isto be transmitted, repeating steps (c) and (d); and (f) marking the endof the data packet by causing the second control line to change from theother state to the first state and releasing control of the NI bus bycausing the first control line to change from the other state to thefirst state.
 8. A communication controller connected to a NI (networkinterface) bus having a packet bus and control lines capable oftransmitting data packets to a device connected to the NI buscomprising:means for obtaining control of the NI bus by causing a firstcontrol line to change from a first binary state to the other binarystate; means for marking the beginning of a data packet by causing asecond control line to change from a first binary state to the otherbinary state; means for writing a byte of data packet information to betransmitted on the packet bus; means for causing a third control linethat functions as a packet clock to change binary states therebyproviding the device with a signal to read the byte of data packetinformation; means for determining if additional data packet informationcomprising the data packet is to be transmitted and causing said writingmeans and said third control line causing means to respectively, writethe additional data on the packet bus and provide the device with asignal to read the additional data; means for marking the end of thedata packet by causing the second control line to change from the otherstate to the first state; and means for releasing control of the NI busby causing the first control line to change from the other state to thefirst state.